1. Technical Field
This invention relates to flow directing structures used within gas turbine engines in general, and to methods and apparatus for inhibiting radial transfer of core gas flow within a core gas flow path in particular.
2. Background Information
A gas turbine engine includes a fan, a compressor, a combustor, and a turbine disposed along a common longitudinal axis. The fan and compressor sections work the air drawn into the engine, increasing the pressure and temperature of the air. Fuel is added to the worked air and the mixture is burned within the combustor. The combustion products and any unburned air subsequently power the turbine and exit the engine producing thrust. The compressor and turbine include a plurality of rotor assemblies and a stationary vane assemblies. Rotor blades and stator vanes are examples of structures (i.e., xe2x80x9cflow directing structuresxe2x80x9d) that direct core gas flow within a gas turbine engine. Air entering the compressor and traveling aft through the combustor and turbine is typically referred to as xe2x80x9ccore gasxe2x80x9d. In and aft of the combustor and turbine, the core gas further includes cooling air entering the flow path and the products of combustion products.
In and aft of the combustor, the high temperature of the core gas requires most components in contact with the core gas be cooled. Components are typically cooled by passing cooling air through the component and allowing it to exit through passages disposed within an external wall of the component. Another cooling technique utilizes a film of cooling air traveling along the surface of a component. The film of cooling air insulates the component from the high temperature core gas and increases the uniformity of cooling along the component surface.
Core gas temperature can vary significantly within the core gas flow path, particularly in the first few stages of the turbine aft of the combustor. On the one hand, core gas temperature decreases as the distance from the combustor increases. On the other hand, core gas temperature typically varies as a function of radial position within the core gas flow path. At a given axial position, the highest core gas temperatures are typically found in the center radial region of the core gas path and the lowest at the core gas path radial boundaries.
Core gas flow anomalies can shift the xe2x80x9chottestxe2x80x9d core gas flow away from the center region of the core gas flow path, toward the liners or platforms that form the core gas inner and outer radial boundaries. An example of such a flow anomaly is a xe2x80x9chorseshoe vortexxe2x80x9d that typically forms where an airfoil abuts a surface; e.g., the junction of the airfoil and platform of a stator vane. The horseshoe vortex begins along the leading edge area of the airfoil traveling away from the center region, toward a wall that forms one of the gas path radial boundaries. The vortex next rolls away from the airfoil and travels along the wall against the core gas flow, subsequently curling around to form the namesake flow pattern. The higher temperature center region core gas flow diverted into close proximity with the wall detrimentally affects the useful life of the wall.
Another example of such a flow anomaly is a xe2x80x9cpassage vortexxe2x80x9d that develops in the passage between adjacent airfoils in a stator or rotor section. The passage vortex is an amalgamation of the pressure side portion of the horseshoe vortex, core gas crossflow between adjacent airfoils, and the entrained air from the freesteam core gas flow passing between the airfoils. Collectively, these flow characteristics encourage some percentage of the flow passing between the airfoils to travel along a helical path (i.e., the xe2x80x9cpassage vortexxe2x80x9d) that diverts core gas flow from the center of the core gas path toward one or both radial boundaries of the core gas path. As in those cases where a horseshoe vortex is present, the higher temperature center core gas flow traveling in close proximity to the walls that form the core gas path radial boundaries detrimentally affects their useful life.
What is needed, therefore, is an apparatus and a method for inhibiting radial transfer of high temperature core gas away from the center radial region of the core gas flow path and toward the inner and outer radial boundaries of the core gas flow path.
It is, therefore, an object of the present invention to provide an apparatus and a method for inhibiting radial transfer of high temperature core gas flow away from the center radial region of a core gas flow path within a gas turbine engine and toward the inner and outer radial boundaries of the core gas flow path.
A method for inhibiting radial transfer of core gas flow away from a center radial region and toward the inner and outer radial boundaries of a core gas flow path within a gas turbine engine is provided that includes the steps of: (1) providing a flow directing structure that includes an airfoil that abuts a wall, said airfoil having a leading edge, a pressure side, and a suction side; and (2) increasing the velocity of the core gas flow in the area where the leading edge of the airfoil abuts the wall. Increasing the velocity of the core gas flow in the area where the leading edge of the airfoil abuts the wall impedes the formation of a pressure gradient along the leading edge area of the airfoil that forces core gas from the center region of the core gas path toward the wall. The apparatus includes means for diverting core gas flow away from the area where the leading edge of the airfoil abuts the wall.
One of the advantages of the present invention is that undesirable high temperature core gas flow from the center region of the core gas path is inhibited from migrating toward the walls that form the inner and outer radial core gas path boundaries. High temperature core gas in close proximity to the walls can detrimentally affect the useful life of the wall. Another advantage of the present invention is that it may be possible to decrease the amount of cooling air necessary to cool the wall. In a conventional stator vane or rotor blade (e.g., examples of flow directing structures), it is known to provide substantial cooling in the wall to counteract the effects of the core gas flow anomaly. Using the present invention, the core gas flow anomaly that forces hot core gas from the center region of the path toward the wall is inhibited. As a result, it may be possible to use less cooling air to satisfactorily cool the wall.